The present invention relates to turbine buckets having an airfoil and a tip shroud carried by the airfoil. More specifically, the present invention relates to edge profiles for a tip shroud.
Turbine buckets typically comprise an airfoil, a platform, a shank and a dovetail. In operation, the dovetail is secured in a complementary slot in a turbine wheel. On many airfoils, integral tip shrouds are used on the outer radial end of the airfoil to create an outer surface of the passage through which the hot gasses must pass. Having the tip shroud as a part of the airfoil typically increases the efficiency of the turbine engine. Moreover, in general, larger tip shrouds enhance engine performance more than smaller ones. As such, in one respect, it is desirable to have the entire outer radial surface of the airfoil covered by a relatively large tip shroud.
During operation, tip shrouds become highly stressed because of the mechanical forces applied to them via the rotational velocity of the turbine engine. The high temperature environment of the turbine coupled with the high stress level quickens the rate at which these parts deform, which shortens their useful life. As a result, it is desirable that tip shroud remain relatively small and light-weight such that operational stresses are reduced. A common practice is to remove certain portions of the tip shroud such that its weight and the resulting operational stresses are reduced while also keeping intact significant portions of the tip shroud profile for the sake of engine performance. When designing tip shrouds, finding the proper balance between these competing objectives—i.e., extended useful part life and efficient engine performance—is a challenge. As such, there is a continuing need for tip shroud edge profiles that effectively meet these dual goals.